How to Find Out Your Boat Gas Tank Size Without the Boat Manual

Knowing your fuel tank size is necessary to fill it with the right amount. In case of a spill, it’s not just about wasting fuel; there is also the matter of exposing ourselves to unnecessary danger. Fortunately, it’s easy to learn how to find out your boat gas tank size.

Referring to your boat manual or placard on the tank is the easiest way, but there are other methods if these are unavailable. Let’s cover a couple of them below.

Keep reading to learn more.

Ways to Find Out Your Boat Gas Tank Size

How Big is My Gas Tank? Two Ways to Find Out

The easiest way to find out how much fuel your tank can hold is to check the vessel’s owner manual for information. If you don’t have one on hand, you can also check the fuel tank, which may have that information printed somewhere on its body.

However, there may be instances where this information is unavailable, and you must determine the figure yourself. There are a couple of ways you can get it.

Method 1: Fill an Empty Tank Using Containers of Known Measurement

What you’ll need:

Fuel source
Fuel containers with known measurement
Wiping cloth
Hose (any kind)

This is a straightforward method. Since it does not involve complicated calculations like the second approach, it may be easier to rely on. However, this solution requires a lot of work.

Step 1: Empty the fuel tank

There are two ways to empty the tank. One way is to drain the contents out, but this may require some technical knowledge or specialized tools, so we’ll leave this discussion for another time.

The second method is something any boater can do on their own; operate the boat until it runs out of juice. It is important to plan your location, as you do not want to end up stranded far from land or the dock.

Step 2: Refuel using containers of known measurement

Fill up your containers with fuel; be sure to use ones with known measurements. Pour the gas into the tank one container at a time until it fills up. Take care not to spill any fuel for better accuracy.

Alternatively, use a hose to siphon the fuel into the tank to ensure there’s no spillage. Here’s how you do it:

Insert one end of the hose into the tank, then insert the other end into your container. Ensure that the hose reaches the bottom of your container, which should be placed higher than the boat’s tank.
Seal up any openings of the container to keep air from getting in; you can use pieces of cloth for this and just hold it in place by hand. The gas will flow out of the container and into the boat tank once the air is kept out.
There may be a bit of fuel left, and you can just pour it yourself. Repeat as needed.

Step 3: Tally the gas consumed

Count the containers you need to fill the boat; subtract how much is left in the last container, if any. Add the total, and this is your boat’s fuel tank size.

Method 2: Calculate The Tank Measurements

What you’ll need:

What you’ll need:

Calculator (online or manual)
Measuring tape

Using this method requires you to have access to your gas tank. This way requires less time to do but needs to factor in the tank’s shape, with irregularly designed tanks being more troublesome to compute.

Step 1: Take your gas tank measurements

Take the fuel tank’s measurements as accurately as possible. Rectangular tanks will need their length, width, and height. Meanwhile, cylindrical ones make use of the height or length depending on their orientation, as well as their diameter.

Step 2: Run the numbers through a boat fuel tank size calculator

While you can make the calculations yourself, different tank shapes require different formulas. Use a tank size calculator to make things easier; select the right shape based on your measurement.

Something to keep in mind; it’s best to leave some space in the tank for air and keep it 90% full at most. Leave some space for the fuel to expand; this also helps avoid spillage.

How Many Gallons of Gas Does a Boat Hold on Average?

Boats have an average boat gas tank size of 40 gallons, but the range begins at around 5-10 GL for small boats, while yacht gas tank size allows up to 350,000 GL.

Let’s look at a few types of vessels and see how much fuel certain models of 20 ft boat hold.

The SunDeck Sport 201 IO Hurricane deck boat gas tank size allows for 47 GL, while the MasterCraft 2023 ProStar ski boat carries only 30 GL.
Even watercraft belonging to the same category may differ significantly in their capacity. A center console boat like the Yamaha 195 FSH Sport maxes out at 40 GL, while Bayliner’s T20CC and T20CX both top out at 55GL.
Bass boat gas tanks usually range between a 25 to 50 GAL For instance, the Skeeter ZX200 has a gas capacity of 36 GL.
Pontoon boat gas tank size ranges from 20 to 35 GL. However, some Pontoon gas tank size can go as low as a mere 5 GL since these are typically for lounging and not actual boating.

Frequently Asked Questions

Why is it important to know your boat’s gas tank size?

The amount of fuel you have directly affects how long your vessel can operate, and knowing the tank size means maximizing its potential. This requires you to learn how to know the size, find the exact figure, and plan your activity well to make the most of any craft.

What are the types of gas tanks?

The two basic types of gas tanks are permanent and portable.

Portable ones are those that can be disconnected and even swapped out. However, these usually have a lower capacity—around 5 GL.
Permanent are those fixed to a spot on the boat, usually on or below deck, and can hold 10 GL and up. It is common for larger vessels to have multiple of these.

How do you calculate the size of a boat’s gas tank?

Aside from running your boat fuel tank’s dimensions through a boat fuel tank size calculator, you can make the calculations yourself. For example, the formula for calculating the volume of a rectangular tank is multiplying its length, width, and height.

This yields your tank’s volume in cubic feet. Convert it to gallons for the standard unit of measurement used in measuring boat fuel capacity. Do so by multiplying the resulting volume by 7.48.

How do you check a gas tank on a boat?

Finding out your boat tank’s size by measuring it requires you to have full access to it. Portable tanks are easy to measure as you only need to disconnect them to take their dimensions. However, a fixed tank can be problematic.

If you can’t access enough of the tank to measure it, use the first method (filling an empty tank and calculating the volumes of fuel used) instead.


Now you know how to find out your boat gas tank size even without access to the owner’s manual. You’ll notice that the boat’s manual contains a lot of essential information, so keep it in a safe place and don’t lose it.

What other measurements or calculations do you know of that are necessary to make when the owner’s manual goes missing? Tell us your suggestions in the comments section below.

Remember to boat safely.

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